Polymers of many different types have been known for many years and have a wide variety of uses. A blend of two or more different polymers each having different properties can increase the applications available to polymers when compared to only unblended polymers. However, blends of polymers that are very dissimilar are, in some instances, not possible due to compatibility problems which prevent the formation of a homogeneous blend. Heterogeneous mixtures of polymers are usually not very useful blends due to phase separation problems during processing detracting from strength and processing properties.
Coupling reagents, also known as compatibilizers, can be polymers containing reactive groups which can form chemical bonds to dissimilar polymers. Thus the reactive group may cause formation of an AB block copolymer which is compatible with both dissimilar polymers. For example a two-phase heterogeneous mixture of polypropylene and some nylons can be made compatible by adding maleated polypropylene. Unreacted amine groups (base) on the nylon react with the succinyl anhydride groups (acid) on the maleated polypropylene to form cyclic imides. The AB block copolymer thus formed contains one block of polypropylene chemically bonded via the imide ring to one block of nylon. Such AB block copolymers serve as compatibilizers for polypropylene and nylon.
The above reaction to form an AB block copolymer is an acid/base (anhydride group/amine group) reaction and works well for attachment of polypropylene to polymers with an excess of unreacted base groups such as amines. However, it is not currently possible to economically couple a polyolefin such as polypropylene to polymers with an excess of unreacted acid groups, such as carboxylic acid groups. See N. C. Liu, H. Q. Xie and W. E. Baker, POLYMER, vol. 34, (#22) page 4680-4687 (1993) for examples of using expensive amines to couple acidic polymers. An attempt to produce this type of coupling agent that would be economical and useful in coupling polyolefins to such polymers involved reacting a diamine (ethylene diamine) with a maleated polyolefin (maleated polypropylene) to provide a polymer having imide rings and unreacted amine groups that could then be available for reacting with polymers containing unreacted acid groups. However, the attempt to produce this coupling agent produced a crosslinked material that was useless as a coupling agent.
U.S. Pat. No. 4,039,560 also tends to infer this result disclosing urea as a cross-linking agent for cellulosics.
In light of the above it would be very desirable to be able to produce a useful non-crosslinked compatibilizing agent or coupling agent that would permit the coupling of polyolefins with polymers containing an excess of unreacted acid groups.